1. Field of the Invention
This invention relates to a valve control device, particularly in an overhead camshaft engine of the type having a rotating cam and a cam drive cooperating with the cam to impart to a valve a reciprocating lifting motion, in opposition to the force exerted by a return spring to close the valve. Internal combustion engine cylinder head valves are currently controlled either directly by the cam via a lifter, or by a rocker arm, itself controlled by the cam directly or by a rod.
2. Description of the Prior Art
These solutions require lubrication by a supply of oil under pressure. This oil must have a viscosity compatible with the operation of other elements of the internal combustion engine and particularly of the bearings, for which this viscosity must preferably remain low.
However, a low viscosity disturbs the operation of the cam because high friction arises due to an extremely small thickness of the oil film located between the cam and the rocker arm or the lifter and due to the low viscosity of this film. The drive torque of the camshaft then becomes very high, particularly for small displacement engines. A further problem is wear, which is speeded up by the presence of combustion wastes including abrasive grains.